EP-A-0 254 510 describes such a handling boom.
In the known prior art, the pivot axis between the manipulation jib and the support frame is placed close to the bottom face of the additional boom, thereby enabling downwards only folding of the additional boom when starting from the configuration in which its manipulation jib extends its support frame. Given the usual dimensions of cranes and of their handling booms, and given the need to avoid allowing the free end of the manipulation jib coming into contact with the ground, the jib can be folded relative to its support frame only when the additional boom is in configurations analogous to that shown in FIG. 2 of the above-mentioned European document, i.e. a configuration in which the first pivot axis is not vertical. As a result, a large force is required to swing the additional boom about said first pivot axis while the additional boom is in its folded configuration, and this force must necessarily be mechanical, e.g. it must be provided by powerful actuators.
In the context of a handling boom having the structure defined under the heading "Field of the Invention", the present invention seeks to make it possible for the first pivot axis to be vertical simultaneously with configurations in which the additional boom is folded, thereby making it possible to reduce the force required for swinging the folded boom about the first pivot axis to substantially the force required for overcoming friction.